QuantXS · Quantum Controlled X-ray Spectroscopy of Elementary Molecular Dynamics

Elementary processes in nature, chemical synthesis, and functional materials critically rely on photochemical transformations. Monitoring these events on the most fundamental level and recording movies of individual molecular motions has been a long-standing dream of chemists and physicists. To this end, time-resolved spectroscopy uses carefully timed sequences of short laser pulses to concatenate stroboscopic frames of information, in analogy to a video camera. This has recently been pushed to the X-ray domain, where ultrabright femto- and attosecond laser pulses enable scientists to monitor nuclear and electronic motions in real-time. However, key features remain elusive due to their intrinsic weakness and the high complexity of their coupled dynamics.My primary goal is to tackle this challenge and develop methods capable of monitoring fundamental molecular photochemistry with unprecedented precision. QuantXS is a theoretical program that puts forward the completely novel concept of quantum-controlled X-ray spectroscopy. I specifically propose to implement pulse shaping techniques at the pump, amplification, and probe stage of time-resolved X-ray measurements. This will tailor the spectroscopic pulse sequence for maximum specificity to so far unmeasured signatures of elementary molecular events. To achieve this, I will implement a bottom-up approach starting with the quantum dynamical simulation of a photochemical ring opening and its transient X-ray signals. I will then use optimal control theory to shape light pulses that (i) maximize the observable absorption, emission, and energy redistribution of existing, weak signatures and bring them above the detection threshold, and (ii) explore entirely new parameter regimes for time-resolved X-ray spectroscopy to generate conceptually new signals. By demonstrating these applications, QuantXS will push ultrafast X-ray sciences to new frontiers in its endeavor to measure the fundamental properties of matter.